前事作废后事无谓
[qián shì zuò fèi hòu shì wú wèi]
This can be translated as the past has been nullified and the future seems insignificant or pointless. This expresses the feeling of someone who thinks there’s no turning back regarding certain matters, whether due to heartbreak or disappointment; it conveys a kind of self-talk and consolation about accepting what’s happened.